1. Field of the Invention
The present invention relates generally to nuclear power reactors, and more particularly, to a seal arrangement and method for sealing an in-core instrument housing (xe2x80x9cICI housingxe2x80x9d) after reinsertion of an in-core instrument (xe2x80x9cICIxe2x80x9d) during a refueling outage.
2. Description of the Related Art
On typical pressurized water nuclear reactors, a plurality of nozzles are located in an organized pattern across the head of a reactor vessel. A majority of the nozzles are used to provide a pressure boundary between neutron absorbing control rods and respective drive mechanisms which provide controlling motion to the control rods. A smaller number of the nozzles are used to provide access into the vessel for ICIs, such as thermocouples and the like.
At every refueling outage for typical nuclear reactors, the ICIs must be partially withdrawn to allow for movement of the fuel. In some cases, the process of withdrawing the ICIs has resulted in damage to the O-ring sealing surfaces of the ICIs and/or the ICI seal housing. In some cases, the sealing surfaces are damaged beyond repair and, because the ICIs have to be reinserted with a reliable seal prior to restarting, the damage must be repaired or an alternate sealing method used.
One currently available option to repair the damaged seal is to reinsert the ICIs without the O-rings, and perform a field seal weld of the ICI to the housing. However, this requires costly and time-consuming field welding. Also, at the next refueling outage, the seal weld must be machined out so that the ICI can be withdrawn, reinserted, and again seal welded. These operations are very time consuming and costly and can only be performed a few times before an alternate method must be used.
Another currently available option to repair the damaged seal is to withdraw the ICI completely and replace the damaged parts. However, because of high radiation contamination, there currently are no methods available to remove the ICI without cutting it up and disposing of the pieces underwater during the withdrawal process. Thus, even a working, undamaged ICI must be discarded and replaced, which is very costly. Moreover, replacement of the seal housing requires field cutting and ASME Code welding, which are very time consuming and costly.
Thus, there is a need for an improved seal arrangement and method for sealing ICI housings after reinsertion of the ICIs during a refueling outage.
It is an object of the present invention to provide a seal arrangement and method for resealing an ICI housing during a refueling outage that allows use of the existing components and minimizes the need for costly field cutting and/or welding, and which can be assembled and disassembled quickly and easily and reused over the life of the plant.
It is a further object of the present invention to provide a seal arrangement for sealing an ICI housing which is economical, efficient and reliable in use, capable of a long operating life, and particularly well adapted for the proposed use.
The present invention provides a seal arrangement for establishing a seal between a nuclear reactor ICI housing and an ICI contained within the ICI housing. The seal arrangement includes a lower seal assembly surrounding an outer portion of the ICI housing, an upper seal assembly surrounding an outer portion of the ICI, a seal housing enclosing the lower and upper seal assemblies, and lower and upper compression assemblies positioned on respective ends of the seal housing. The compression assemblies each include a drive nut and a compression collar. The compression collars engage and apply an axial load on the seal assemblies to maintain a reliable seal between the seal housing and the outer portion of the ICI housing, and between the seal housing and the outer portion of the ICI. Variations in the construction and methods for installing the seal arrangements to the ICI housing and ICI are disclosed.
According to a broad aspect of the present invention, a seal arrangement for a nuclear reactor ICI housing is provided, comprising: a first seal assembly surrounding an outer portion of an ICI housing; a second seal assembly surrounding an outer portion of an ICI inserted within the ICI housing; a seal housing having first and second ends, the seal housing enclosing the first and second seal assemblies; and first and second compression assemblies positioned on and engaging the first and second ends of the seal housing, respectively.
According to another broad aspect of the present invention, a seal arrangement is provided in combination with a nuclear reactor ICI housing and an ICI inserted within the ICI housing. The seal arrangement comprises: a first seal assembly surrounding an outer portion of the ICI housing; a second seal assembly surrounding an outer portion of the ICI; a seal housing having first and second ends, the seal housing enclosing the first and second seal assemblies; and first and second compression assemblies positioned on the first and second ends of the seal housing, respectively. The first compression assembly engages the first seal assembly to maintain a seal between the first end of the seal housing and the outer portion of the ICI housing. The second compression assembly engages the second seal assembly to maintain a seal between the second end of the seal housing and the outer portion of the ICI.
According to another broad aspect of the present invention, a method of sealing a nuclear reactor ICI housing is provided, comprising the steps of: positioning a first compression assembly and first seal assembly around an outer portion of the ICI housing; positioning a seal housing over an end of the ICI housing; positioning a second seal assembly and second compression assembly around an outer portion of an ICI contained within the ICI housing; and threading respective drive nuts of the first and second compression assemblies onto the seal housing to maintain a compressive sealing force against the first and second seal assemblies.